The present invention relates generally to an introducer system having dilatation capabilities to facilitate insertion of a medical device into a body tissue, including a patient""s vascular system. More particularly, the introducer protects the medical device from damage and the body tissue from trauma during insertion.
Catheters or cannulas with relatively large diameters are commonly used in various surgical procedures, which include draining fluid from a body cavity, delivering fluid to a body tissue, and introducing surgical and diagnostic tools. To access a body tissue for insertion of these large catheters or cannulas, a guidewire is traditionally used, as described by Seldinger in Br. J. 2(6026):21-22 (1976), incorporated herein by reference in its entirety. For example, to insert an internal jugular cannula to provide venous drainage for cardiopulmonary bypass during coronary artery bypass grafting surgery, a patient""s right internal jugular vein is first punctured by a small diameter needle. A guidewire is then inserted through the needle into the internal jugular vein. The needle is withdrawn, leaving the guidewire in the blood vessel. A dilator is inserted over the guidewire into the puncture site to enlarge the opening into the internal jugular vein. The dilator is removed and the venous drainage cannula is inserted over the guidewire into the internal jugular vein. After final placement of the cannula, the guidewire is removed, leaving the cannula in the internal jugular vein and available to drain venous blood to a cardiopulmonary bypass machine. In this approach, dilators are used to enlarge an opening on the body tissue for inserting cannulas, and therefore, often traumatize the body tissue.
To reduce the trauma associated with these access devices, thin wall construction using elastomeric materials has been attempted. However, access devices formed of these materials possess a tendency to buckle or bulge during insertion. To overcome the problem of buckling and folding, an adjustable vascular introducer formed of a rolled up plastic sheath in tube form surrounded by a coaxial elastic sheath was described in Cardiovasc. Intervent. Radiol. 2:169-171 (1989), incorporated herein by reference in its entirety. This device would expand around the oversized portion of a balloon catheter as it passed through the device. This adjustable introducer, however, has an expandable circular cross-section which limits its applicability beyond balloon valvuloplasty.
Other introduction devices which utilize a trocar or dilator inside a straight or curved cannula to facilitate insertion of the cannula have been described in Klyce et al., U.S. Pat. No. 4,863,430, incorporated herein by reference. Although these devices simplify the steps for inserting a cannula, they lack the ability to protect the cannula, especially when mounted with fragile, exposed, external balloons, from damage during insertion.
A need therefore exists for an introducer system which provides dilation capabilities to facilitate insertion of a medical device into a body tissue, and provides protection for the device and the body tissue from trauma during insertion.
The present invention provides an introducer system having the ability to dilate an incision on a body tissue for insertion of a medical device, said introducer further having the ability to protect the medical devices and body tissue from injury during insertion. The introducer system comprises an elongate shaft having a proximal and a distal end. A flexible sleeve is mounted on the distal end of the shaft. When the shaft is positioned within a lumen of a cannula, having a proximal end, a distal end, and a lumen therebetween, the sleeve is adapted to circumferentially cover the outer surface of the distal end of the cannula. The flexible sleeve, which is typically also expandable, may be constructed using elastomeric or lubricious material. The elongate shaft may be made of flexible material, e.g. plastic. In certain embodiments, the shaft may include a coil which also provides flexibility for the shaft.
In an alternative embodiment, the proximal end of the shaft may have a collet and a screw lock proximal to the collet adapted for securing the introducer in the lumen of a cannula. The screw and collet also provide a hemostatic seal for the cannula. The distal end of the elongate shaft may include an angulated tip which enlarges an opening into a body tissue, thereby facilitating insertion of a cannula.
The present invention also provides methods for introducing a cannula into a body tissue, including a patient""s blood vessel. The methods employ an introducer insertable within a lumen of the cannula, said introducer having a proximal and distal end, and a flexible sleeve mounted on the distal end of the shaft and adapted to cover a distal end of the cannula. After an incision is made on the body tissue, the distal end of the cannula is inserted through the incision into the body tissue with the sleeve covering the outer surface of the distal end of the cannula. This feature is particularly significant in a cannula having an expandable balloon mounted at its distal end in that the balloon is protected from being punctured by the sometimes-calcific plaque of a vessel wall. After final placement of the cannula, the elongate shaft is retracted, whereby the sleeve is inverted and drawn into the lumen of the cannula, thereby removing the sleeve from the outer surface of the distal end of the cannula. The shaft and sleeve are subsequently withdrawn from the lumen of the cannula.
It will be understood that there are many advantages to using an introducer/dilator with balloon protection as disclosed herein. For example, the introducer of the present invention provides (1) dilatation capability, thereby obviating the need for another dilator, (2) a flexible shaft which can be easily accommodated in any curved or straight cannula, (3) protection for a body tissue from trauma during insertion, (4) protection for a medical device from being damaged during insertion, (5) a shaft and sleeve which are easily removed after final placement of the medical device, and (6) a restraint on the outer diameter of the medical device which helps to minimize the crosssectional profile of the device for insertion into a vessel or other body tissue.